skip to main content

This content will become publicly available on December 31, 2022

Title: Harmonization of global surface ocean pCO2 mapped products and their flux calculations; an improved estimate of the ocean carbon sink
Air-sea flux of carbon dioxide (CO2) is a critical component of the global carbon cycle and the climate system with the ocean removing about a quarter of the CO2 emitted into the atmosphere by human activities over the last decade. A common approach to estimate this net flux of CO2 across the air-sea interface is the use of surface ocean CO2 observations and the computation of the flux through a bulk parameterization approach. Yet, the details for how this is done in order to arrive at a global ocean CO2 uptake estimate varies greatly, unnecessarily enhancing the uncertainties. Here we reduce some of these uncertainties by harmonizing an ensemble of products that interpolate surface ocean CO2 bservations to near global coverage. We propose a common methodology to fill in missing areas in the products and to calculate fluxes and present a new estimate of the net flux. The ensemble data product, SeaFlux (Gregor & Fay (2021), doi.org/10.5281/zenodo.4133802, https://github.com/luke-gregor/SeaFlux), accounts for the diversity of the underlying mapping methodologies. Utilizing six 30 global observation-based mapping products (CMEMS-FFNN, CSIR-ML6, JENA-MLS, JMA-MLR, MPI-SOMFFN, NIESFNN), the SeaFlux ensemble approach adjusts for methodological inconsistencies in flux calculations that can result in an average error of 15% more » in global mean flux estimates. We address differences in spatial coverage of the surface ocean CO2 between the mapping products which ultimately yields an increase in CO2 uptake of up to 19% for some products. Fluxes are calculated using three wind products (CCMPv2, ERA5, and JRA55). Application of an appropriately scaled gas exchange 35 coefficient has a greater impact on the resulting flux than solely the choice of wind product. With these adjustments, we derive an improved ensemble of surface ocean pCO2 and air-sea carbon flux estimates. The SeaFlux ensemble suggests a global mean uptake of CO2 from the atmosphere of 1.92 +/- 0.35 PgC yr-1. This work aims to support the community effort to perform model-data intercomparisons which will help to identify missing fluxes as we strive to close the global carbon budget. « less
Authors:
; ; ; ; ; ; ; ; ;
Editors:
Elger, Kirsten; Carlson, David; Klump, Jens; Peng, Ge
Award ID(s):
1850983
Publication Date:
NSF-PAR ID:
10293980
Journal Name:
Earth system science data
ISSN:
1866-3508
Sponsoring Org:
National Science Foundation
More Like this
  1. The Southern Ocean plays an important role in determining atmospheric carbon dioxide (CO 2 ), yet estimates of air-sea CO 2 flux for the region diverge widely. In this study, we constrained Southern Ocean air-sea CO 2 exchange by relating fluxes to horizontal and vertical CO 2 gradients in atmospheric transport models and applying atmospheric observations of these gradients to estimate fluxes. Aircraft-based measurements of the vertical atmospheric CO 2 gradient provide robust flux constraints. We found an annual mean flux of –0.53 ± 0.23 petagrams of carbon per year (net uptake) south of 45°S during the period 2009–2018. This is consistent with the mean of atmospheric inversion estimates and surface-ocean partial pressure of CO 2 ( P co 2 )–based products, but our data indicate stronger annual mean uptake than suggested by recent interpretations of profiling float observations.
  2. Abstract

    This study investigates the formation mechanism of the ocean surface warming pattern in response to a doubling CO2with a focus on the role of ocean heat uptake (or ocean surface heat flux change, ΔQnet). We demonstrate that thetransientpatterns of surface warming and rainfall change simulated by the dynamic ocean–atmosphere coupled model (DOM) can be reproduced by theequilibriumsolutions of the slab ocean–atmosphere coupled model (SOM) simulations when forced with the DOM ΔQnetdistribution. The SOM is then used as a diagnostic inverse modeling tool to decompose the CO2-induced thermodynamic warming effect and the ΔQnet(ocean heat uptake)–induced cooling effect. As ΔQnetis largely positive (i.e., downward into the ocean) in the subpolar oceans and weakly negative at the equator, its cooling effect is strongly polar amplified and opposes the CO2warming, reducing the net warming response especially over Antarctica. For the same reason, the ΔQnet-induced cooling effect contributes significantly to the equatorially enhanced warming in all three ocean basins, while the CO2warming effect plays a role in the equatorial warming of the eastern Pacific. The spatially varying component of ΔQnet, although globally averaged to zero, can effectively rectify and lead to decreased global mean surface temperature of a comparable magnitude as the global meanmore »ΔQneteffect under transient climate change. Our study highlights the importance of air–sea interaction in the surface warming pattern formation and the key role of ocean heat uptake pattern.

    « less
  3. Keynote points • Thermal expansion from a warming ocean and land ice melt are the main causes of the accelerating global rise in the mean sea level. • Global warming is also affecting many circulation systems. The Atlantic meridional overturning circulation has already weakened and will most likely continue to do so in the future. The impacts of ocean circulation changes include a regional rise in sea levels, changes in the nutrient distribution and carbon uptake of the ocean and feedbacks with the atmosphere, such as altering the distribution of precipitation. • More than 90 per cent of the heat from global warming is stored in the global ocean. Oceans have exhibited robust warming since the 1950s from the surface to a depth of 2,000 m. The proportion of ocean heat content has more than doubled since the 1990s compared with long-term trends. Ocean warming can be seen in most of the global ocean, with a few regions exhibiting long-term cooling. • The ocean shows a marked pattern of salinity changes in multidecadal observations, with surface and subsurface patterns providing clear evidence of a water cycle amplification over the ocean. That is manifested in enhanced salinities in the near-surface, high-salinitymore »subtropical regions and freshening in the low-salinity regions such as the West Pacific Warm Pool and the poles. • An increase in atmospheric CO2 levels, and a subsequent increase in carbon in the oceans, has changed the chemistry of the oceans to include changes to pH and aragonite saturation. A more carbon-enriched marine environment, especially when coupled with other environmental stressors, has been demonstrated through field studies and experiments to have negative impacts on a wide range of organisms, in particular those that form calcium carbonate shells, and alter biodiversity and ecosystem structure. • Decades of oxygen observations allow for robust trend analyses. Long-term measurements have shown decreases in dissolved oxygen concentrations for most ocean regions and the expansion of oxygen-depleted zones. A temperature-driven solubility decrease is responsible for most near-surface oxygen loss, though oxygen decrease is not limited to the upper ocean and is present throughout the water column in many areas. • Total sea ice extent has been declining rapidly in the Arctic, but trends are insignificant in the Antarctic. In the Arctic, the summer trends are most striking in the Pacific sector of the Arctic Ocean, while, in the Antarctic, the summer trends show increases in the Weddell Sea and decreases in the West Antarctic sector of the Southern Ocean. Variations in sea ice extent result from changes in wind and ocean currents.« less
  4. Abstract. Interannual variations in air–sea fluxes of carbon dioxide (CO2) impactthe global carbon cycle and climate system, and previous studies suggest thatthese variations may be predictable in the near term (from a year to a decadein advance). Here, we quantify and understand the sources of near-termpredictability and predictive skill in air–sea CO2 flux on global andregional scales by analyzing output from a novel set of retrospective decadalforecasts of an Earth system model. These forecasts exhibit the potential topredict year-to-year variations in the globally integrated air–sea CO2flux several years in advance, as indicated by the high correlation of theforecasts with a model reconstruction of past CO2 flux evolution. Thispotential predictability exceeds that obtained solely from foreknowledge ofvariations in external forcing or a simple persistence forecast, with thelongest-lasting forecast enhancement in the subantarctic Southern Ocean andthe northern North Atlantic. Potential predictability in CO2 fluxvariations is largely driven by predictability in the surface ocean partialpressure of CO2, which itself is a function of predictability in surfaceocean dissolved inorganic carbon and alkalinity. The potentialpredictability, however, is not realized as predictive skill, as indicated bythe moderate to low correlation of the forecasts with anobservationally based CO2 flux product. Nevertheless,more »our results suggestthat year-to-year variations in ocean carbon uptake have the potential to bepredicted well in advance and establish a precedent for forecasting air–seaCO2 flux in the near future.

    « less
  5. Abstract. Significant rates of primary production occur in the oligotrophic ocean, without any measurable nutrients present in the mixed layer, fueling a scientific paradox that has lasted for decades. Here, we provide a new determination of the annual mean physical supply of nitrate to the euphotic zone in the western subtropical North Atlantic. We combine a 3-year time series of measurements of tritiugenic 3He from 2003 to 2006 in the surface ocean at the Bermuda Atlantic Time-series Study (BATS) site with a sophisticated noble gas calibrated air–sea gas exchange model to constrain the 3He flux across the sea–air interface, which must closely mirror the upward 3He flux into the euphotic zone. The product of the 3He flux and the observed subsurface nitrate–3He relationship provides an estimate of the minimum rate of new production in the BATS region. We also apply the gas model to an earlier time series of 3He measurements at BATS in order to recalculate new production fluxes for the 1985 to 1988 time period. The observations, despite an almost 3-fold difference in the nitrate–3He relationship, yield a roughly consistent estimate of nitrate flux. In particular, the nitrate flux from 2003 to 2006 is estimated to be 0.65more »± 0.14 mol m−2 yr−1, which is ~40 % smaller than the calculated flux for the period from 1985 to 1988. The difference in nitrate flux between the time periods may be signifying a real difference in new production resulting from changes in subtropical mode water formation. Overall, the nitrate flux is larger than most estimates of export fluxes or net community production fluxes made locally for the BATS site, which is likely a reflection of the larger spatial scale covered by the 3He technique and potentially also by the decoupling of 3He and nitrate during the obduction of water masses from the main thermocline into the upper ocean. The upward nitrate flux is certainly large enough to support observed rates of primary production at BATS and more generally in the oligotrophic subtropical ocean.« less